Paraoxonases (PON), a family of orphan enzymes with multiple enzyme activities assigned to them, comprise of three proteins PON1, PON2, and PON3. The aryl esterase, organophosphatase, and lipo-lactonase activities of PON enzymes underscore their importance in inflammation, toxicology, and infection, respectively. Epidemiological studies identified PON proteins in the etiology of a number of inflammatory diseases including cardiovascular diseases. Sequence analysis of PON genes suggest that the PON family evolved by gene duplication with PON2 being the first and PON1 the most recent member. Interestingly, PON2 and PON3 are predominantly localized to intracellular compartments while PON1 is found exclusively extracellular and associated solely with HDL particles. Our laboratory has cloned and characterized both PON2 and PON3 genes, and also developed mouse models for studying the role of PON2 and PON3 in atherosclerosis. Recent studies suggest that PON2 and PON3 are associated with mitochondria and mitochondrial associated membranes and play important roles in the modulation of mitochondrial oxidative stress. PON2 protects against the development of atherosclerosis and insulin resistance. Moreover, macrophage PON2 plays a critical role in the mechanisms that mediate both the development of atherosclerosis and insulin resistance. PON3 protects against the development of atherosclerosis and obesity. Despite the role of PON2 and PON3 in critical cellular functions and associated pathologies, the physiological substrates and molecular mechanisms by which PON2 and PON3 function as anti-atherogenic and anti-inflammatory proteins are largely unknown. In this application, we propose to i. delineate the physiological substrates for PON2 and PON3 proteins, ii. determine the molecular mechanisms by which PON2 and PON3 function, and iii. to examine the role of PON2 and PON3 proteins in vascular inflammatory diseases including diabetes, obesity, and ischemic heart disease. These studies will help identify novel molecular targets for the treatment of inflammatory diseases